Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/tests/slack-import-test-direct-messages.json

@@ -0,0 +1,34 @@
+[
+    {
+        "id": "D24TJMP61",
+        "created": "1472131245",
+        "members": [
+            "U1VVY70HK",
+            "U1W4XLR62"
+        ]
+    },
+    {
+        "id": "D24TJNXUG",
+        "created": "1472132335",
+        "members": [
+            "U1XG9JUH1",
+            "U20APGU90"
+        ]
+    },
+    {
+        "id": "D24TLE5V5",
+        "created": "1472131113",
+        "members": [
+            "U1TQ3A3L7",
+            "U1URR19QV"
+        ]
+    },
+    {
+        "id": "D24TM4MPT",
+        "created": "1472131021",
+        "members": [
+            "U1V47GAM9",
+            "U1XVNP6DT"
+        ]
+    }
+]